This invention relates to fiber optic light carrying probes and more particularly to a light carrying probe suitable for curing resins in medical, scientific, industrial amd military applications. The probe is also suitable for providing light during surgical or diagnostic procedures to enhance an operator's perceptions. Thus, the probe also has use in, for example, gynecological procedures.
Resins (restoratives, dental composites and other materials) exposed to high intensity visible light change in form from a paste-like putty to a substance having the hardness of ceramic or glass in a short amount of time. Using this procedure, the standard amount of time to cure restoratives applied to one tooth is approximately ten seconds. The time could be extended, depending on the area and depth of applied restorative, up to sixty seconds. This dental (orthodontic) procedure is relatively new. Generally, the technique is referred to as bonding. By using this technique, which is primarily cosmetic, gaps between the teeth, fillings and cracked or chipped defects can be repaired. Furthermore, color can be matched so that teeth can be restored to their natural look. The teeth (especially the front upper/lower teeth) can also be laminated with a thin layer of this restorative which comes in more than fifty different shades and colors. After hardening (i.e., curing with high intensity light, which is normally provided by fiber optics), the teeth are then reshaped and polished. The probe is not limited, in the medical field, to curing dental resins. For example, it may be used for curing resins used during plastic or reconstructive surgery and in fact may be used in curing most any bone composite.
Originally, the most commonly used fiber optic light carrier was fiber optic cables in lengths from four feet to nine feet, and bundle sizes from 5.0 mm to 7 mm. These cables were plugged into high intensity light sources so that the light would be transmitted through the cable. This apparatus is being gradually replaced by a more practical fiber optic light curing gun coupled to a short fiber optic probe of various lengths and diameters. The probe normally has a bent tip to improve maneuverability in difficult access areas. The gun includes a high intensity fan cooled light source mounted directly inside of the gun enclosure.
The fibre optic probe has been made typically in two different ways. The first involves filling a stainless steel sheath with conventional non-coherent light transmitting glass fibers. This approach is not very effective because the stainless steel tube cannot be adequately packed to produce optimum light transmission. That is, only up to 80% of the tube space can be filled with light transmitting fibers due to, for example, unavoidable gaps between individual fibers.
The second approach produces a sheathed glass cladded fiber optic rod with improved light transmission efficiency. Instead of using conventional fibers to transmit the light, the second approach incorporates a coherent fiber rod. The rod has a packing fraction of over 90% and thus transmits considerably more light than the probe within the scope of the first approach. Improved light transmission, i.e., efficiency, is preferred for a number of reasons. For example, such would reduce curing times. A curing time reduction would, for example, have obvious benefits during dental "bonding" procedures which would include reducing operator fatigue and patient discomfort. To produce the rod, a bundle of large diameter fibers are inserted into clear glass cladding and that assembly drawn to size while heat is applied. During this process, the fibers are fused together while being sealed in the glass cladding. The glass cladded rod is then cut, bent and then sheathed to prevent light leakage along the length of the rod.
The sheathing, which must be capable of withstanding repeated autoclaving due to the obvious need for sterilization before medical use to avoid the transmission of communicable diseases (e.g., AIDS), primarily functions to prevent light leakage. That is, if the high intensity light was allowed to leak from the probe, the operator and operator's assistants could be distracted and thereby error in delicate medical and non-medical procedures. Furthermore, the high intensity light reaching the patient's, operators's or operator's assistant's eyes not only could cause discomfort, but create harmful effects on the physiological make-up of the eye. Thus, even though the sheath increases manufacturing costs, it is evident that it is an essential component of the prior art.
Unfortunately, due to manufacturing considerations, a one-piece sheath is impractical. Stainless steel is appropriate to resolve sterilizing considerations, but inappropriate to sheath a rigid bent rod. First, it would not be feasible to insert the rigid bent glass cladded rod into the rigid stainless steel tube. Furthermore, the difference in melting points between the glass cladded rods and the stainless steel tubing renders the insertion of a given rod into stainless steel tubing, prior to the heating and bending operation, impractical. As a result, high temperature flexible silicon is used to sheath the bent portion, while the straight portion is encased in stainless steel.
Even though the silicon sheath provides rod protection due to its shock absorbing characteristics and survives autoclaving operations better than other suitable elastomers, the silicon sheath design has drawbacks. First, the two-piece sheath construction increases a manufacturer's material acquisition and inventory costs when compared to the requirements for making a glass cladded rod encased within a single piece sheath. Furthermore, the assembly of a two-piece sheath requires more manufacturing steps which can also increase the cost of the probe.
Other drawbacks of the silicon sheath become apparent after repeated sterilization of the probe. That is, the silicon degenerates after repeated autoclaving operations permitting light leakage and inhibiting sterilizability. The silicon sheath shrinks when subjected to the high autoclaving temperatures. Because, the glass cladded rod is rigid, the silicon circumferentially stretches, radially shrinks, develops pockets and gaps, and separates from adjacent probe structure to release the stresses. These pockets, gaps and separations permit light leakage. For example, the fit-up (designated at numeral 25 in FIG. 3) between the silicon sheath and adjacent stainless steel sheath 23 or endfitting 27 degenerates, creating a source for undesirable light leakage. The silicon sheath degeneration also provides a means for trapping bacteria or other infectious matter. For example, because the silicon sheath cannot be permanently sealed to the glass cladding, it is held thereto by friction fit. The silicon sheath then separates from the cladding as it degenerates. The bacteria trapped between the silicon sheath and glass cladded rod, due to the above separation, is not completely removed when the probe is autoclaved. Therefore, the probe becomes a means to transfer communicable diseases (e.g., AIDS) from patient to patient or patient to doctor and so forth. This problem is exacerbated when the probe is used in medical procedures where bleeding is inevitable.